The present disclosure is related to a zoom lens which can be utilized in electronic cameras such as a digital camera, a video camera, a broadcast camera, a cinematic camera, a surveillance camera, etc., and to an imaging apparatus equipped with this zoom lens.
The zoom lenses disclosed in Japanese Unexamined Patent Publication Nos. 2013-221999 and 2012-013817 are proposed as zoom lenses to be employed in electronic cameras such as a digital camera, a video camera, a broadcast camera, a cinematic camera, a surveillance camera, etc.
Conventional broadcast cameras perform imaging according to the HD (High Definition) standard, and the maximum resolution thereof had been Full HD (1920×1080 pixels). Recently, there are many cameras which are compatible with the 4K standard (3840×2160 pixels, for example) which has approximately four times the number of pixels of Full HD, and imaging employing such cameras is increasing. Further, there are cameras which are compatible with the Super High Vision standard, which has an even greater number of pixels than 4K. High performance lenses are desired for these high pixel number cameras.
However, the lenses disclosed in Japanese Unexamined Patent Publication No. 2013-221999 include many having comparatively wide angles of view, but it cannot be said that these lenses sufficiently correct aberrations. In addition, the lenses disclosed in Japanese Unexamined Patent Publication No. 2012-013817 have sufficiently wide angles of view, but it cannot be said that the lenses are sufficiently miniaturized with respect to image size.
The present disclosure has been developed in view of the foregoing circumstances. The present disclosure provides a high performance zoom lens which is compact, has a wide angle of view, and favorably corrects various aberrations. The present disclosure also provides an imaging apparatus equipped with this zoom lens.
A zoom lens of the present disclosure consists of, in order from the object side to the image side:
a first lens group having a positive refractive power, which is fixed when changing magnification;
at least two moving lens groups that move to change the distance among adjacent lens groups in the direction of the optical axis when changing magnification; and
a final lens group having a positive refractive power, which is fixed when changing magnification;
the first lens group consisting of, in order from the object side to the image side: a 1a lens group having a negative refractive power which is fixed during focusing operations; a 1b lens group having a positive refractive power which moves during focusing operations; and a 1c lens group having a positive refractive power which is fixed during focusing operations; and
the 1a lens group including at least one negative lens that satisfies Conditional Formulae (1), (2), and (3) below62<νd1an  (1)0.65<θgF1an+0.001625·νd1an<0.7  (2)3<f1an/f1a<7  (3)
wherein νd1an is the Abbe's number with respect to the d line of the negative lens within the 1a lens group, θgF1an is the partial dispersion of the negative lens within the 1a lens group, f1an is the focal length with respect to the d line of the negative lens within the 1a lens group, and f1a is the focal length with respect to the d line of the 1a lens group.
Note that it is more preferable for any one or any combination of Conditional Formulae (1-1), (2-1), and (3-1) below to be satisfied in addition to Conditional Formulae (1), (2), and (3).70<νd1an<100  (1-1)0.66<θgF1an+0.001625·νd1an<0.69  (2-1)4<f1an/f1a<6  (3-1)
In addition, it is preferable for Conditional Formula (4) below to be satisfied. Note that it is more preferable for Conditional Formula (4-1) below to be satisfied.8<f1c/fw<24  (4)9<f1c/fw<21  (4-1)                wherein f1c is the focal length with respect to the d line of the 1c lens group, and fw is the focal length with respect to the d line of the entire lens system at the wide angle end.        
In addition, it is preferable for the 1a lens group to satisfy Conditional Formulae (5), (6), and (7) below. Note that it is more preferable for any one or any combination of Conditional Formulae (5-1), (6-1), and (7-1) below to be satisfied in addition to Conditional Formulae (5), (6), and (7).νd1ap<40  (5)20<νd1ap<39  (5-1)0.62<θgF1ap+0.001625·νd1ap<0.67  (6)0.63<θgF1ap+0.001625·νd1ap<0.66  (6-1)0.4<f1ap/f1<2  (7)0.5<f1ap/f1<1.5  (7-1)
wherein νd1ap is the Abbe's number with respect to the d line of a positive lens within the 1a lens group, θgF1ap is the partial dispersion of the positive lens within the 1a lens group, f1ap is the focal length with respect to the d line of the positive lens within the 1a lens group, and f1 is the focal length with respect to the d line of the first lens group.
In addition, the at least two moving lens groups may consist of, in order from the object side to the image side, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power. Alternatively, the at least two moving lens groups may consist of, in order from the object side to the image side, a second lens group having a negative refractive power, and a third lens group having a negative refractive power.
As a further alternative, the at least two moving lens groups may consist of, in order from the object side to the image side, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a negative refractive power. In this case, it is preferable for Conditional Formula (8) below to be satisfied. Note that it is more preferable for Conditional Formula (8-1) below to be satisfied.1.7<DL3/DL2<20  (8)2.1<DL3/DL2<17  (8-1)
wherein DL3 is the range of movement of the third lens group, and DL2 is the range of movement of the second lens group.
Here, the “range of movement” refers to the amount of displacement from the position most toward object side to the position most toward the image side of each lens group when changing magnification from the wide angle end to the telephoto end.
In addition, in the case that the moving lens groups consist of three lens groups which are positive, negative, and negative as described above, it is more preferable for Conditional Formula (9) below to be satisfied. Note that it is more preferable for Conditional Formula (9-1) below to be satisfied.0.4<f3/f4<0.8  (9)0.5<f3/f4<0.7  (9-1)
wherein f3 is the focal length with respect to the d line of the third lens group, and f4 is the focal length with respect to the d line of the fourth lens group.
In addition, in the case that the moving lens groups consist of three lens groups which are positive, negative, and negative as described above, it is preferable for the third lens group to have two cemented lenses, for at least one of the cemented lenses to consist of a positive lens and a negative lens, and for Conditional Formula (10) below to be satisfied. In this case, it is preferable for the cemented lens provided most toward the image side within the third lens group to satisfy Conditional Formula (10). Note that it is more preferable for Conditional Formula (10-1) to be satisfied.0<νd3p−νd3n<10  (10)4<νd3p−νd3n<10  (10-1)
wherein νd3p is the Abbe's number with respect to the d line of the positive lens of the cemented lens consisting of a positive lens and a negative lens within the third lens group, and νd3p is the Abbe's number with respect to the d line of the negative lens of the cemented lens consisting of a positive lens and a negative lens within the third lens group.
An imaging apparatus of the present disclosure is equipped with the zoom lens of the present disclosure described above.
Note that the above expression “consists of” means that lenses that practically have no power, optical elements other than lenses such as a stop, a mask, a cover glass, and filters, and mechanical components such as lens flanges, a lens barrel, an imaging element, a camera shake correcting mechanism, etc. may be included, in addition to the constituent elements listed above.
In addition, the surface shapes and the signs of the refractive powers of the lenses described above are considered in the paraxial region in cases that aspherical surfaces are included.
The zoom lens of the present disclosure consists of, in order from the object side to the image side: a first lens group having a positive refractive power, which is fixed when changing magnification; at least two moving lens groups that move to change the distance among adjacent lens groups in the direction of the optical axis when changing magnification; and a final lens group having a positive refractive power, which is fixed when changing magnification. The first lens group consists of, in order from the object side to the image side: a 1a lens group having a negative refractive power which is fixed during focusing operations; a 1b lens group having a positive refractive power which moves during focusing operations; and a 1c lens group having a positive refractive power which is fixed during focusing operations. The 1a lens group includes at least one negative lens that satisfies Conditional Formulae (1), (2), and (3) below. Therefore, it is possible to realize a high performance zoom lens which is compact, has a wide angle of view, and favorably corrects various aberrations.62<νd1an  (1)0.65<θgF1an+0.001625·νd1an<0.7  (2)3<f1an/f1a<7  (3)
In addition, the imaging apparatus of the present disclosure is equipped with the zoom lens of the present disclosure. Therefore, the imaging apparatus of the present disclosure can be miniaturized, and is capable of obtaining wide angle images having high image quality.